JPH0898488A - Three-phase brushless motor - Google Patents

Abstract

PURPOSE: To reduce the difference between maximum and minimum torques generated from a three-phase brushless motor. CONSTITUTION: A Groove 5a having axially elongated cross-section are made in the circumferential center of each pole of a permanent magnet 5 constituting a rotor thus providing a low flux density region. In other words, the flux density at a position shifted by 90 deg. electric angle from a border point a1 between S and N poles is set lower than that of a normal permanent magnet having no groove 5a. Furthermore, three-phase exciting coils are driven through a drive circuit, i.e., a three-phase exciting circuit for feeding the exciting currents constantly to all exciting coils.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a three-phase brushless motor, and more particularly, it is intended to minimize fluctuations in output torque with respect to rotational position.

[0002]

2. Description of the Related Art A three-phase brushless motor in which an S-pole and an N-pole are alternately magnetized on the outer peripheral surface in the circumferential direction at equal intervals and surrounded by a three-phase exciting coil is surrounded by a three-phase brushless motor. Compared with this, a stable output torque can be obtained, so that response to various fields is expected. And the conventional 3
The magnetic flux density distribution of the permanent magnets forming the rotor of the phase brushless motor is sinusoidal as shown in FIG. 10A, or trapezoidal as shown in FIG. 10B by devising the magnetization. Was becoming.

[0003]

SUMMARY OF THE INVENTION Here, the conventional three-phase block is used.
In the lathless motor, three-phase exciting coils a, b and
c is star-connected in a Y shape, and the coils a to c are shown in FIG.
Supply an exciting current as shown (ie 60 electrical degrees
It is driven by a two-phase excitation method that switches the energization state every time.)
And the torque generated in each coil is
When the bundle density distribution is sinusoidal as shown in FIG.
As shown in the lower part of 2, changes depending on the rotational position of the rotor
It becomes to draw a mountain-shaped waveform. And each of them
The torque generated in the motor is the torque generated in the motor.
Therefore, the torque of the motor is as shown in the upper part of FIG.
It changes depending on the rotational position of the rotor. in this case,
Torque ripple (maximum torque value T_maxAnd the minimum value T_min
Difference difference ΔT = T_max-T _min) Is the average torque (=
(T_max+ T_min) / 2) about 15%
It

It can be said that such a torque ripple is smaller than that of other types of brushless motors. However, considering that the torque ripple is used as a drive source of a power steering device of an automobile, for example, torque fluctuations in the steering system are caused by the driver. It is preferable to be as small as possible in order to make the steering feel uncomfortable.
A torque ripple of about 5% is too uncomfortable, and it has been desired to further reduce the torque ripple.

The present invention has been made in view of the above-mentioned unsolved problems of the conventional technique, and an object thereof is to provide a three-phase brushless motor in which torque ripple is minimized.

[0006]

In order to achieve the above object, the present invention provides a rotatable rotor in which S poles and N poles are alternately magnetized in the circumferential direction in the circumferential direction at equal intervals, and a star. A three-phase brushless motor comprising: three-phase exciting coils connected to each other and surrounding the outer peripheral surface of the rotor; and a drive circuit for supplying an exciting current to the three-phase exciting coils. The drive circuit is a three-phase excitation drive circuit that constantly supplies some excitation current to all of the three-phase excitation coils, and a low magnetic flux density region is formed at the circumferential center position of each magnetic pole of the rotor.

[0007]

In the three-phase brushless motor of the present invention, since the drive circuit is a three-phase excitation drive circuit, some excitation current is always supplied to all three-phase excitation coils, unlike two-phase excitation. . Therefore, even when the phase of one exciting coil is switched, the exciting current flows through the other two exciting coils, so that the output torque of the motor does not drop when the phases are switched, and smooth switching is performed.

In the case of three-phase excitation drive, the position where the motor torque, which is the sum of the torques generated in the coils, becomes maximum is the circumferential center position (S) of the region magnetized to the S pole and the N pole. (Position of 90 degrees in electrical angle from the boundary between the pole and N pole)
Although the coil is opposite to the coil, a low magnetic flux density region is formed at the center position in the circumferential direction, and accordingly, the maximum value of the torque of the motor is reduced and the torque ripple is reduced.

The method of forming the low magnetic flux density region is not particularly limited, and it is possible, for example, to devise the magnetization, or to appropriately form a concave portion or a void in the circumferential center position of the permanent magnet. It is also possible by forming.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a front sectional view showing the structure of a three-phase brushless motor 1 according to the first embodiment of the present invention. That is, the three-phase brushless motor 1 includes a cylindrical housing 2 and
Bearings 3a, 3 arranged along the axis of the housing 2
a rotating shaft 4 rotatable by b, a permanent magnet 5 for driving a motor fixed to the rotating shaft 4, and a three-phase exciting coil fixed to the inner peripheral surface of the housing 2 so as to surround the permanent magnet 5. 6a, 6b and 6c are wound around the stator 6, and the rotary shaft 4 and the permanent magnet 5 are provided.
A rotatable rotor 7 is formed by.

A ring-shaped permanent magnet 8 for phase detection is fixed to the rotor 7 close to one end of the rotary shaft 4, and the permanent magnet 8 has an S pole and an N pole. The poles are magnetized alternately in the circumferential direction at equal intervals. On the other hand, on the inner end surface of the housing 2 on the side where the bearing 3b is disposed, a support substrate 10 made of a ring-shaped thin plate is provided via a stay 9 so that the insulating portion on the inside faces the permanent magnet 8. On the surface of the support substrate 10 facing the permanent magnet 8 side, the phase detection element 11 made of, for example, a Hall element is fixed so as to face the permanent magnet 8. In addition, the phase detection element 11 is actually the excitation coils 6a to 6b.
Three of them are provided at appropriate intervals in the circumferential direction according to the driving timing of 1. However, since FIG. 1 is a sectional view, only one of them is shown.

The rotational position of the rotor 7 is recognized by utilizing the fact that the output of each phase detecting element 11 changes depending on the magnetic pole of the permanent magnet 8 facing the phase detecting element 11, and the drive circuit, which will be described later, responds accordingly by recognizing the rotational position of the rotor 7. The exciting current supplied to 6a to 6c is switched to drive the rotor 7 to rotate appropriately. On the other hand, as shown in FIG. 2, which is a plan view showing the magnetized state, the permanent magnets 5 constituting the rotor 7 are magnetized such that three S poles and three N poles are alternately arranged in the circumferential direction at equal intervals. Has been done.

However, at the center position in the circumferential direction of each magnetic pole of the permanent magnet 5 of this embodiment, a concave groove 5 having a semicircular cross section which is long in the axial direction is formed.
a is formed so that the center position in the circumferential direction of each magnetic pole is a low magnetic flux density region. That is, S pole and N
The magnetic flux density at positions 90 degrees away from the pole boundary point a ₁ by an electrical angle is lower than that of a normal permanent magnet having no groove 5a, and the electrical angle is 0.
As shown by the solid line in FIG. 3, the magnetic flux density distribution in the range of ˜360 degrees is recessed at positions of 90 degrees and 270 degrees in electrical angle as compared with the normal magnetic flux density distribution shown by the broken line that changes sinusoidally. The distribution is as follows.

On the other hand, the three-phase exciting coils 6a to 6c are star-connected in a Y-shape as shown in FIG. 4, and are arranged so as to surround the outer peripheral surface of the rotor 7 from three sides separated by 120 degrees. The drive circuit 15 for supplying the exciting current to the exciting coils 6a to 6c, as shown in FIG.
Six transistors (field effect transistors) _Tu , T
It is composed of _v , T _w , T _u ′, T _v ′, T _w ′.

[0015] Specifically, the transistor T _u -T _u are in series relation ', transistor T _v -T _v', as well as arranged in parallel between the transistors T _w -T _w both terminals respectively of the power of the ' , The transistors T _u −T _u ′, the transistors T _v −T _v ′, and the transistors T _w −T _w ′ are connected to the outer ends of the exciting coils 6a, 6b, 6c (opposite to the center of the star connection). Side).

[0016] Then, the gate voltage of each transistor T _u through T _w 'is adapted to be controlled by the output of the phase detector device 11 described above. Here, the drive circuit 15 of the present embodiment is a three-phase excitation drive circuit that drives the three-phase brushless motor 1 by constantly supplying an excitation current to all of the three-phase excitation coils 6a to 6c. Each exciting coil 6a
The direction and magnitude of the exciting current to 6c are, specifically,
Is as shown in FIG. 5, the timing of on / off of each transistor T _u through T _w 'as 3-phase excitation drive circuit,
It is as shown in Table 1 below. However, in Table 1, "1" represents ON and "0" represents OFF.

[0017]

[Table 1]

For example, if it is at the position of d in FIG. 5,
Since it corresponds to the section of Table 1, the upper transistors T _u and T _w and the lower transistor T _v ′ are turned on, and the other transistors are turned off, so that the exciting coils 6 a and 6 c are respectively from the outer end side. A current having a magnitude of I / 2 flows, and a current having a magnitude of I flows from the connection side to the exciting coil 6c. Also in the other sections ~, each exciting coil 6a ~ according to ON / OFF of each transistor.
A current having a magnitude of I or I / 2 flows through 6c.

With such a three-phase excitation drive, even when the phase is switched, the current continues to flow from the upper stage to the lower stage through at least two coils, so that the current is not interrupted. On the other hand, in the two-phase excitation drive, as shown in FIG. 11, when switching the phases, there is a momentary break between the upper stage and the lower stage, and there is a momentary time when no current flows. However, the rise of the current was delayed and the output of the motor dropped, and smooth switching was not performed.

That is, if the three-phase excitation drive is adopted as in this embodiment, the torque generated in the exciting coils 6a to 6c can be prevented from instantaneously dropping, so that the torque generated in the exciting coils 6a to 6c can be prevented. It is possible to prevent the minimum value T _min of the motor torque, which is the sum of the above, from dropping. If the magnetic flux density distribution of the permanent magnet 5 is as shown in FIG. 3 and the magnitude of the current flowing through the exciting coils 6a-6c is as shown in FIG. 5, the torque generated in each exciting coil 6a-6c is , Is proportional to the product of the amount of magnetic flux orthogonal to each of the exciting coils 6a to 6c and the exciting current flowing in each of the exciting coils 6a to 6c. .

For example, with respect to the coil 6a, since the magnitude of the current is I / 2 during the electrical angle from 0 degree to 60 degrees, the generated torque gradually increases.
When the degree is exceeded, the magnitude of the electric current becomes I, so that the generated torque instantaneously doubles, and from there, it tries to gradually increase again. However, since the magnetic flux density distribution around 90 degrees is concave, the torque generated in the coil 6a once becomes small, gradually rises after 90 degrees, and drops slightly before 120 degrees. Then, when the temperature reaches 120 degrees, the magnitude of the current returns to I / 2, and the magnitude of the torque generated instantaneously becomes 1/2, and then gradually decreases to zero at 180 degrees. , 180 degrees, a reverse current flows through the exciting coil 6a,
The generated torque gradually increases again. The change in the torque of the exciting coil 6a between 180 and 360 degrees is 0 to
It is the same as the torque change during 180 degrees, and the torque change of the exciting coil 6b is exactly the same as the torque change of the exciting coil 6a except that it is delayed by 120 degrees.
Similarly, the torque change of the exciting coil 6c is
It is exactly the same except that the torque change of a is delayed by 240 degrees.

Since the torque generated in the three-phase brushless motor 1 is the sum of the torques generated in the exciting coils 6a to 6c, it has a waveform as shown by the solid line in the upper part of FIG. Here, originally, the magnetic flux density is 5
Since it becomes highest at the circumferential center position of each magnetic pole, the torque generated in each exciting coil 6a to 6c becomes the largest at the corresponding position, and the torque generated in the three-phase brushless motor 1 also becomes large. It should be maximum at the same position as the torque generated at.

However, in this embodiment, since the concave groove 5a is formed at the position where the maximum torque is generated, the maximum value T _max of the motor torque becomes small. Thus, with the configuration of this embodiment, the minimum value T of the motor torque is
_{Since min} can be prevented from falling and the maximum value T _max of the motor torque can be reduced, the torque ripple determined by the difference between them can be suppressed. By the way, the present inventor has found that the electrical angle of the permanent magnet 5 is 90 degrees.
When the torque of the three-phase brushless motor 1 in which the magnetic flux density around 20 degrees and 270 degrees is reduced by about 20% is actually measured, the torque ripple is about 5%, which is about 1 / the conventional value.
It was confirmed to be reduced to about 3. Therefore, the three-phase brushless motor as in this embodiment is suitable as a drive source for an electric power steering device of a vehicle, for example.

FIG. 7 is a view showing a second embodiment of the present invention and is a plan view of the permanent magnet 5 as in FIG. 2 of the first embodiment. Since the other construction is the same as that of the first embodiment, its illustration and description are omitted. That is, in the present embodiment, the six permanent magnets 5A to 5F of the same shape having a fan-shaped flat cross section in which the S poles and the N poles are arranged in the circumferential direction are arranged so as to surround the rotation shaft 4 (see FIG. 1). A permanent magnet 5 equivalent to that of the embodiment is constructed. However, in the adjacent permanent magnets 5A to 5F, the same poles are in contact with each other.

Then, chamfers 5b are formed on the outer peripheral surface side ends of the permanent magnets 5A to 5F. Therefore, when the permanent magnets 5A to 5F are combined as shown in FIG. 7, the chamfered portions 5b of the adjacent permanent magnets 5A to 5F cause a low magnetic flux at a position of 90 degrees in electrical angle from the boundary between the S pole and the N pole. The density area is formed. Therefore, even with the configuration of this embodiment, it is possible to obtain the same effects as the first embodiment. Moreover, since the low magnetic flux density region can be formed by flattening the corner portions of each of the permanent magnets 5A to 5F, the manufacturing cost can be reduced as compared with the configuration of the first embodiment in which the groove processing is required. There is an advantage. In the low magnetic flux density region, a desired shape may be formed by molding from the beginning, instead of cutting the corners of the permanent magnets 5A to 5F.

FIG. 8 is a diagram showing a third embodiment of the present invention, and is a plan view of the permanent magnet 5 as in FIG. 2 of the first embodiment. Since the other construction is the same as that of the first embodiment, its illustration and description are omitted. That is, in this embodiment, as in the second embodiment, the S pole and the N pole are arranged in the circumferential direction.
Six permanent magnets 5A to 5 of the same shape having a fan-shaped cross section with poles lined up
Fs are arranged so as to surround the rotary shaft 4 (see FIG. 1) to form a permanent magnet 5 equivalent to that of the first embodiment.

However, in this embodiment, each of the permanent magnets 5A ...
The circumferential dimension of the permanent magnets 5A to 5F is set to be slightly smaller than 1/6 of the circumferential dimension of the permanent magnet 5 in the first embodiment so that a slight gap 5c is formed between the 5Fs. . Also in the present embodiment, the adjacent permanent magnets 5A to 5A.
At 5F, the same poles face each other. Therefore, when the permanent magnets 5A to 5F are combined as shown in FIG. 8, the gap 5c forms a low magnetic flux density region at a position at an electrical angle of 90 degrees from the boundary between the S pole and the N pole. Therefore, even with the configuration of this embodiment, the first
It is possible to obtain the same effect as that of the embodiment. Moreover,
Since it is not necessary to chamfer the permanent magnets 5A to 5F, there is an advantage that the manufacturing cost can be further reduced as compared with the second embodiment.

FIG. 9 is a view showing a fourth embodiment of the present invention, and is a plan view of the permanent magnet 5 as in FIG. 2 of the first embodiment. Since the other construction is the same as that of the first embodiment, its illustration and description are omitted. That is, in this embodiment, a circular hole 5d that is long in the axial direction is formed in the portion close to the outer peripheral surface at the center position in the circumferential direction of each magnetic pole of the permanent magnet 5 similar to that in the first embodiment. A low magnetic flux density region is formed at a position at an electrical angle of 90 degrees from the boundary between the S pole and the N pole. Therefore, even with the configuration of this embodiment, it is possible to obtain the same effects as the first embodiment.

In each of the above embodiments, the shape of the permanent magnet 5 is appropriately devised to form a low magnetic flux density region at a position of an electrical angle of 90 degrees from the boundary between the S pole and the N pole. However, even if the permanent magnet 5 is not processed, the low magnetic flux density region may be formed by devising the magnetization, for example. In addition, in the configuration of each of the above embodiments,
In order to maintain the impact resistance of the processed permanent magnet 5, the periphery of the permanent magnet 5 may be covered with a cylindrical cover.

[0030]

As described above, according to the present invention,
In a three-phase brushless motor, the drive circuit is a three-phase excitation drive circuit, and a low magnetic flux density region is formed at the center position in the circumferential direction of each magnetic pole of the rotor. In addition to being able to prevent it, the maximum value of the torque can be reduced, so that the torque ripple can be suppressed.

[Brief description of drawings]

FIG. 1 is a front sectional view of a three-phase brushless motor according to a first embodiment of the present invention.

FIG. 2 is a plan view of the permanent magnet of the first embodiment.

FIG. 3 is a distribution diagram of magnetic flux density according to the first embodiment.

FIG. 4 is a circuit diagram showing a connection state of an exciting coil and a drive circuit.

FIG. 5 is a waveform diagram of an exciting current.

FIG. 6 is a waveform diagram of torque generated in each exciting coil and motor.

FIG. 7 is a plan view of a permanent magnet of a second embodiment.

FIG. 8 is a plan view of a permanent magnet of a third embodiment.

FIG. 9 is a plan view of a permanent magnet according to a fourth embodiment.

FIG. 10 is a conventional magnetic flux density distribution diagram.

FIG. 11 is a waveform diagram of a conventional exciting current.

FIG. 12 is a waveform diagram of torque generated in each conventional excitation coil and motor.

[Explanation of symbols]

 1 3 Phase Brushless Motor 4 Rotating Shaft 5 Permanent Magnet 5A to 5F Permanent Magnet 5a Recessed Groove 5b Chamfer 5c Gap 5d Circular Hole 6a to 6c Excitation Coil 7 Rotor 15 Drive Circuit

Claims (1)

[Claims] 1. A rotatable rotor in which S poles and N poles are magnetized alternately and equidistantly in the circumferential direction on the outer peripheral surface, and the rotor is arranged in star connection so as to surround the outer peripheral surface of the rotor. In a three-phase brushless motor including a three-phase exciting coil and a drive circuit that supplies an exciting current to these three-phase exciting coils, the drive circuit constantly supplies some exciting current to all of the three-phase exciting coils. Is a three-phase excitation drive circuit for supplying a low magnetic flux density region in the circumferential center position of each magnetic pole of the rotor.